I have debian 3-16.0-4 amd64/GNOME3/Libreofiice 188.8.131.52/
after installing xournal (and all the dependencies) I noticed the following problem in libreofiice( and also in gedit).
When I open libreoffice from command line using sudo, then the dead keys are working, but if I opened it as a regular user dead keys are not working.
Similar for the gedit,firefox,terminal. It seems that is not a libreoffice problem. But it would help if I knew where libreoffice is looking for the dead keys combinations when it starts.